This invention relates to a method of creating a curved surface of a three-dimensional body, and more particularly to a method of the type described that is ideal for the preparation of a numerical control tape required for the numerically controlled machining of a three-dimensional metal mold or the like.
A curved surface of a three-dimensional metal mold or the like, when drawn out on the plane of a blueprint is generally represented by a plurality of given section curves, but no data is shown for the shapes of the areas lying between the adjacent given section curves. When machining the workpiece in accordance with the numerical control method, however, it is essential that the adjacent section curves should be connected smoothly despite the absence of the data indicating the shape of the surface between them. In other words, this means that machining must be performed by generating the curved surface lying between the adjacent section curves from such data as that indicative of the given section curves, punching a numerical control (NC) tape so as to include the data concerning the generated curved surface, and then machining the workpiece in accordance with the instructions on the NC tape. To this end, the NC tape ordinarily is prepared by using a computer, and either of two systems can be adopted to create the desired curved surfaces. The first is a batch system in which processing is effected by dividing a curved surface into minute portions. In the second system a two-dimensional curve made up of straight lines and arcs is modified for each minute displacement applied to a third axis, i.e. the axis of the third dimension. The first system, however, entails the processing of large quantities of data as well as highly complicated mathematical processing, and requires a large-scale computer system. The second system makes processing with a small scale computer possible, but there is no three-dimensional tool offset capability and an excessive limitation upon tool movement direction and machining shape, making it impossible to create sophisticated three-dimensional bodies.